The present invention relates to a butterfly valve having a throttle plate adapted to be rotated between open and closed positions within a throat of the valve. More particularly, the present invention relates to such a valve in which the throttle plate is centered by an adjustable thrust bearing acting against a spring loaded thrust bearing located on the opposite side of the throttle plate.
Butterfly valves are employed in many well known machines and devices for controlling flow conditions within a passageway. For instance, butterfly valves are employed for throttling purposes within an automotive carburetor. As another example, butterfly valves are employed for throttling purposes in connection with vacuum process chambers that are used to provide a pressure controlled manufacturing environment such as required in the manufacturing of semiconductors.
A butterfly valve comprises a throttle plate located within a throat of the valve. The throttle plate is rotatable between a closed position in which the throat of the valve is obstructed and an open position in which the throat is open. Generally, in the prior art, the throttle plate is attached to a rotatable shaft with screws. Rotation of the shaft rotates the throttle plate within the valve throat. In case of a vacuum process chamber, the screws can present a contamination hazard or an incompatibility with the process or process environment. In addition, the shaft and screws can produce turbulence in the flow. Although there are many different shaft mountings employed in the art, carbon filled, teflon bearings are often used where the butterfly valve is to undergo many cycles of operation. End plugs bear against the ends of the shaft to center the throttle plate within the valve throat. Such end plugs add to the complexity and expense involved in manufacturing the valve. Additionally, after repeated cycling of the valve, the end plugs tend to wear out. This is particularly critical for a butterfly valve used in a vacuum process chamber because the valve tolerances can be very tight, with very minute clearances between the throttle plate and valve throat.
As will be discussed the present invention provides a butterfly valve designed for simplicity and cost effectiveness in its construction and its maintenance.